This invention relates to chemical protective coverings. More specifically, the invention relates to materials and articles that can be used to afford protection of persons or contents from noxious or harmful chemicals in the form of vapors, aerosols, or particulates. The chemical protective coverings provided in accordance with the invention are particularly suitable for applications such as articles of clothing, tents, sleeping bags, and the like.
Chemical protective coverings are intended to prevent harmful levels of chemicals existing in an external environment from reaching the user or wearer or contents of said materials.
Chemical protective clothing is worn when the surrounding environment may present a potential hazard of exposing an individual to harmful or noxious chemicals. Historically the materials used in protective clothing have had to trade off protection for comfort. That is, those offering more protection were unacceptably uncomfortable, and those being of satisfactory comfort did not offer acceptable protection.
For example, one approach which is known in the art, is to interpose what is generally referred to as an xe2x80x9cimpermeablexe2x80x9d material between the wearer and the hazardous environment. A suitable material of this type will exhibit low permeability to harmful chemicals and yet be pliable enough to be employed in a garment or other article of clothing application. An example of this approach would be a glove utilizing butyl rubber as the barrier to harmful chemicals.
Although such materials may provide adequate protection from harmful chemicals by significantly restricting the passage of such agents, these materials also characteristically prevent the passage of water vapor. A material that to a great extent prevents the transmission of water vapor is termed non-breathable.
When used as protective coverings for people, non-breathable materials retard the human body""s process of heat dissipation normally achieved through the evaporation of perspiration. Without significant transmission of water vapor, or breathability, prolonged use-of-such materials can result in intolerable discomfort and even death of the wearer. The discomfort will initially result from high levels of moisture generated by the wearer building up within the protective covering, followed by the heat stresses imposed upon the wearer due to the lack of evaporative cooling. This can progress to heat stroke, and eventually death. Thus, these types of materials may offer satisfactory protection, but unsatisfactory comfort. This problematic characteristic of non-breathable protective covering materials makes them unsuitable for anything more than very short duration usage or limited areas of coverage.
Conversely, many covering materials that possess significant water vapor transmission rates, for instance many woven textiles or nonwoven polyolefin materials, will not provide desired levels of protection to harmful or noxious chemicals. That is, these types of materials may offer satisfactory comfort, but unsatisfactory protection.
Various efforts have been made to address in more favorable terms the trade-off between protection and comfort.
One such effort, well known in the art, involves the use of adsorptive materials which are interposed between the wearer and the contaminated environment such as described in U.S. Pat. No. 4,510,193 by Blucher, Blucher, and de Ruiter.
Adsorptive chemical protective systems work by adsorbing hazardous liquids and vapors into sorbants, thus inhibiting them from reaching that which the systems are intended to protect. One limiting characteristic of sorbants is that they possess a finite capacity to adsorb chemicals. A second limiting characteristic of sorbants is that they will indiscriminately adsorb chemical species for which protection is unnecessary, thus reducing the available capacity for adsorption of the chemicals to which they were intended to provide protection.
The finite capacity and indiscriminate adsorption characteristics of adsorptive systems limit their duration of use and storage life. Adsorptive systems will begin to adsorb various chemical vapor contaminants present in the atmosphere upon exposure, thus progressively reducing their available capacity over time. This limits their duration of use. This process can even occur when the adsorptive systems are kept within sealed packages over long spans of time. This limits the storage life of such materials.
Additionally, the finite capacity and indiscriminate adsorption characteristics necessitate the incorporation of relatively large quantities of sorptive elements within a chemical protective covering in order to achieve and sustain adequate levels of protection. This can result in thick and heavy barrier systems that can have high resistances to heat and moisture transfer and can impose undesirable physiological stresses on the wearer. Thus, adsorptive systems are also restricted by a trade-off between protection and comfort.
Furthermore, increased bulk and weight are also undesired characteristics for the packaging, storage, handling, and transportation of these materials.
A more preferred approach to creating chemical protective coverings that provide satisfactory comfort and protection relies on the use of selectively permeable materials. Materials that are selectively permeable exhibit a significant preferential permeability to specific chemical species. This approach can allow the creation of protective coverings that facilitate the transmission of desired chemical species while restricting the passage of undesired chemical species. Particularly for articles of chemical protective clothing, it would be desirable for a selectively permeable material to have preferential permeability towards water vapor relative to noxious or harmful vapors. That is, the permeability to water vapor is to be substantially greater than the permeability to noxious or harmful vapors. This can provide the basis for protective coverings that will be comfortable while at the same time being highly protective.
As the protective function of selectively permeable materials is not dependent upon sorption of chemicals, they are not bound by the limitations intrinsic to adsorptive systems. Unlike adsorptive systems, which rely upon a significant mass and thickness of appropriate materials to provide adequate and sustained protection, selectively permeable materials, free of these limitations, can be made extremely thin and lightweight. This facilitates the creation of much less bulky and lighter protective garments and accessories.
Regardless of the type of protective covering material employed, it is likely to be exposed in use to differing and frequently varying conditions of humidity and temperature. For example, a wearer of a protective article of clothing will generate varying amounts of heat and moisture internal to the protective covering depending upon the physiological stresses imposed upon the wearer. External to the protective covering, the conditions will vary due to natural motivations such as weather conditions, or human influenced conditions such as could be found within a vehicle or man-made structure. Thus, it is to be expected that a protective covering will be exposed to a wide range of conditions during its use, which must be considered in the design and application of any protective covering material.
These conditions can influence the performance of selectively permeable materials. Selectively permeable materials that possess the desirable quality of high water vapor transmission are generally hydrophilic polymers. As such, their moisture content will be influenced by the relative humidity of their surroundings. As the surrounding relative humidity of such a selectively permeable material changes, the moisture level within the selectively permeable material will also change. In general, it is observed that these materials are more permeable to many chemical vapors at high relative humidity, and conversely are less permeable to many chemical vapors at low relative humidity. Thus, when such materials are employed in chemical protective covering applications, it is important to consider the protective characteristics of these materials over the range of relative humidities which are to be expected during use. Particularly, it is important to consider the permeation of noxious or harmful chemicals under conditions of high humidification. High resistance to the permeation of chemical vapors at conditions of mild relative humidity may not be representative of performance at elevated conditions of relative humidity.
For the applications under consideration, it would be desirable to reduce the permeability to noxious or harmful chemical vapors, particularly at high relative humidity, without an undesirable reduction in the permeation of water vapor. Similarly, it would be desirable to increase the permeation of water vapor, without an undesirable increase in the permeability to noxious or harmful chemical vapors, particularly at high relative humidity.
Thus, to be most useful in protective coverings, selectively permeable materials must provide good breathability and must provide low permeability to hazardous chemicals, particularly at the difficult condition of high relative humidity. Additionally, it is desirable to improve the breathability of such materials without significantly diminishing their protective performance, and to improve their protective performance without significantly diminishing their breathability.
A number of selectively permeable materials have been investigated for general use in these applications. These include a variety of films using cellulose-based polymers such as described in U.S. Pat. No. 5,743,775 by Ulrich Baurmeister and assigned to Akzo Nobel NV as well as porous polyamide films as detailed in U.S. Pat. No. 5,824,405 by Lloyd Steven White and assigned to W.R. Grace and Co. It has also been taught that good breathability and good resistance to hazardous chemicals can be achieved under some conditions using a polyalkyleneimine protective material as described in U.S. Pat. No. 5,391,426 by Huey S. Wu. However, the chemical permeation characteristics of each of these materials are evaluated under relatively low relative humidities that do not represent the range of conditions that would be encountered in use. The performance of these materials will be limited by their compromise between protection and comfort, particularly at elevated relative humidity.
Surprisingly, as taught herein, it has been discovered that the performance of a selectively permeable chemical protective covering based upon a polyamine polymer can be considerably and unexpectedly enhanced by incorporating amine-acid moieties within the polyamine polymer. Unexpectedly, it has been discovered that the water vapor transmission rate may be made substantially better without a comparable trade-off in protective qualities, particularly at elevated relative humidity. Further, it has been discovered that the resistance to noxious or harmful chemicals, particularly at conditions of elevated relative humidity, may be made substantially better without a comparable trade-off in water vapor transmission. And most surprisingly, it has been discovered that the ideal can be achieved wherein both the water vapor transmission rate and the resistance to noxious or harmful chemicals even at elevated conditions of relative humidity may be improved simultaneously, resulting in selectively permeable materials capable of concurrently providing improved comfort with improved protection.
Accordingly, it is an object of this invention to provide lightweight and pliable selectively permeable materials that exhibit high degrees of breathability in conjunction with protection over a wide range of conditions. It is an object of the present invention to provide a selectively permeable protective covering capable of transmitting high quantities of water vapor while also being capable of adequately restricting the passage of noxious or harmful chemical vapors, even under conditions of high humidification. The chemical protective covering of this invention may be used for chemical protective articles of clothing that are comfortable because of their ability to allow the efficient evaporation of perspiration via transmission of water vapor and are suitable for application in a broad range of conditions likely to be encountered in realistic use scenarios.
In its broadest aspect, the chemical protective and water vapor permeable covering of this invention comprises a selectively permeable sheet of a polyamine polymer wherein at least 10% of the polyamine polymer amines are amine-acid moieties wherein the acidic species of said amine-acid moieties have a pKa less than 6.4. The materials are selected and adjusted via experimentation to achieve a chemical protective covering which has a water vapor transmission rate greater than 2,000 g/(m2*day) and a permeability to bis-2-chloroethyl sulfide of less than 0.02 cm/sec, preferably less than 0.002 cm/sec, and more preferably less than 0.0002 cm/sec.
In one embodiment, the polyamine polymer with amine-acid moieties is part of a selectively permeable composite sheet where the polyamine polymer forms a substantially continuous layer residing essentially on the surface of a water vapor permeable substrate which may be an open pore substrate, a closed pore substrate, or a void-free substrate.
In further embodiments of the invention, the polyamine polymer with amine-acid moieties is part of a selectively permeable composite sheet with an open pore substrate, where at least a portion of the polyamine polymer resides within the substrate.
In another embodiment of the invention, the chemical protective covering is comprised of two water vapor permeable open pore polytetrafluoroethylene substrates and a polyalkyleneimine-containing polyamine polymer with amine-acid moieties specifically involving H2SO4 and at least 25% of the polyamine polymer amines. These materials are made to form a selectively permeable composite sheet where the polyamine polymer forms a substantially continuous layer residing between the substrates, with at least a portion of the polyamine polymer residing within each substrate.
The invention is particularly useful as or within articles of clothing such as garments, gloves, footwear, and the like.